The invention relates to a process and to a plant for pickling steel strips.
According to conventional processes, hot and cold strips of steel are treated in continuous annealing and pickling lines. In this procedure the belt in coiled form ,--,--; is unwound off an uncoiling hasp and connected to the end of a preceding coil in a welding machine. In order to avoid stoppages in the plant and resultant over-pickling of the preceding belt ,--,--; the strip is withdrawn during the stationary period of the belt in the uncoiling section from a strip store means. The incoming strip is first annealed in an annealing oven ,--,--; cooled with air and water, whereafter the scale is removed in a pickling plant. A large variety of methods for pickling a hot or cold strip has found acceptance in the industry, the best known method being pickling with neutral electrolyte followed by mixed acid post-treatment. In this context ,--,--; mixed acid denotes a mixture of nitric and hydrofluoric acid. After rinsing ,--,--; the strip is dried and recoiled. The resulting welding seams are cut out in this process, resulting once again in a coil of approximately the same length as when entering the plant. This process suffers from drawbacks amongst which primarily a high plant investment and labor input as well as large space requirements are to be mentioned.
As compared with the use of other pickling processes, particularly in,,relation to the passage of the strip through the plant ,--,--; a general technical misconception existed that the conventional material might cause damage to the strip. In particular ,--,--; it was feared that the brick linings of pickling vessels might result in scratching or similar impairment of the strip, this in particular when pickling stainless steel strip.
On the other hand ,--,--; materials are needed for lining the pickling plant which are capable of withstanding the chemical attack by the treatment chemicals as well as the mechanical wear and tear. Mechanical linings of brick and ceramics, although resistant to chemical attacks, frequently result in damage to the surface of the pickled product or are themselves not capable of readily withstanding mechanical wear and tear.